Piston



FIG. 1 is a perspective view of the piston;

FIG. 2 is a top view of the piston;

FIG. 3 is a side view of the piston;

FIG. 4 is cross-sectional view of the piston taken along line 4-4 of FIG. 5;

FIG. 5 is a side view of the piston rotated 90 degrees from FIG. 3;

FIG. 6 is cross-sectional view of the piston taken along line 6-6 of FIG. 3;

FIG. 7 is a bottom view of the piston; and,

FIG. 8 is a bottom perspective view of the piston. 

CLAIM We claim the ornamental design for a piston, as shown and described. 